403Nb叶片钢高温热压缩静态再结晶研究

利用Gleeble-3500热模拟试验机对403Nb马氏体叶片钢进行二道次高温热压缩试验,对不同温度、应变速率、道次间隔下发生的静态再结晶进行了研究和计算,得到403Nb静态再结晶、静态再结晶激活能和静态再结晶晶粒尺寸模型。     

Dynamic and Static Recrystallization Behaviour of Coarse-grained Austenite in a Nb-V-Ti Microalloyed Steel简

The dynamic recrystallization （DRX） and static recrystallization （SRX） behaviour of coarse-grained aus- tenite in a Nb-V-Ti microalloyed steel were studied by using a Gleeble thermomechanical simulator. Continuous and interrupted compression tests of coarse-grained austenite were performed in the temperature range of 1000-1 150 ℃ at a strain rate of 0. 1- 5 s 1. The peak and critical strains for the onset of DRX were identified with strain hardening rate analysis, and the ratio of critical strain to peak strain was found to be consistent with the one reported for fine- grained austenite. An equation of the time for 50% softening was proposed by considering the activation energy of steel without microalloying elements and the solute drag effect of microalloying elements. Strain-induced precipitation may not take place at the deformation temperature above 1000 ℃, which indicates that SRX of coarse-grained aus- tenite is mainly retarded by coarse grain size and Nb in solution during rough rolling.     

Description of Austenite Recrystallization Kinetics During Low-Alloy Steel Hot Deformation

Metallurgist - Mathematical analysis of experimental data for low-alloy steel 09G2S austenite recrystallization after hot rolling is provided. An original mathematical model is proposed that...     

高铌微合金钢高温变形流变应力预测模型

 以流变应力曲线的唯象特征和本构方程的传统理论为基础,针对高铌微合金钢开发出一种新的描述高温变形应力 应变曲线的数学模型。该模型包括两个基本方程,确立了应力与应变、温度、变形速率的数学关系,预测了加工硬化和动态再结晶各阶段流变应力的变化,预测结果与实验结果吻合良好。     

Static Recrystallization Kinetics Model After Hot Deformation of Low-Alloy Steel Q345B

The static recrystallization behavior of low-alloy steel Q345B during double-pass hot compression deformation tests was investigated in the temperature range of 900-1000 ℃,the true strain range of 0.15-0.25 and the interpass time range of 0.5-50 s on Gleeble-3500 thermo-simulation machine.The results show that static recrystallization during the interpass time is observed.As the deformation temperature and strain increase,softening caused by static recrystallization is obvious.According to the analysis and calculation of thermo-simulation data,the static recrystallization activation energy was obtained and static recrystallization kinetics model was built.Finally,the error analysis of static recrystallization kinetics model proved that the model had good accuracy.Therefore,this model provides a theoretical basis for static recrystallization(SRX)and will contribute to the development of multipass hot rolling process,in order to control the rolling process more accurately.     

Modelling the Kinetics of Austenite Decomposition in Nb‐Ti‐V Microalloyed Steel after Hot Strip Rolling

In hot strip rolling of Nb‐microalloyed steels the austenite transformation usually starts in the hot run‐out table (HRT) under a high cooling rate and finishes while the strip is coiled, when the cooling rate is much slower. Thus the transformation takes place during a two‐step‐cooling regime. This paper presents a mathematical model able to predict such transformation. The experimental alloy used here was a Nb‐V‐Ti microalloyed steel. The model employs an Avrami type equation associated with the additivity rule. The time constant b in the Avrami equation was expressed as a function of parameters A and B whereas the time exponent n was best modelled as a constant of value 1. Experiments have shown that the constants A and B are linearly dependent. An artificial neural network (ANN) model was used to predict B. The ANN model takes into account the following process variables: austenite deformation applied above the non‐recrystallization temperature (Tnr), deformation applied below Tnr, cooling rate in the HRT, and coiling temperature. From the results it was proposed that the transformation is governed by early site saturation, diffusion being the only operating mechanism. This conclusion was based on the experiment value found for n and on the need of a single temperature dependent parameter, either A or B, to predict the course of the overall austenite transformation.     

Precipitation of Nb in Ferrite After Austenite Conditioning. Part I: Microstructural Characterization

While the role of Nb during the processing of austenite is quite clear, what happens in subsequent stages to the concentration of this element left in solution is subject to some debate. In particular, some uncertainty still subsists concerning the eventual homogeneous precipitation in Nb supersaturated polygonal ferrite. The present work was aimed at clarifying the precipitation sequence of Nb during coiling, through a systematic work and a careful selection of the processing conditions in order to produce different scenarios concerning the initial state of Nb. A Nb-microalloyed steel was thermomechanically processed in the laboratory followed by simulated coiling at different temperatures in the 873?K to 1023?K (600?°C to 750?°C) range. Transmission electron microscopy (TEM) showed interphase precipitation of NbC at high coiling temperatures, while at 873?K (600?°C), homogeneous general precipitation took place in ferrite and followed a Baker?CNutting orientation relationship.     

含Nb微合金钢Q345E热变形行为研究

通过Thermecmaster-Z热模拟机研究了(%)0.084C-1.05Mn-0.026Nb-0.003Ti-0.007Mo-0.003V微合金钢Q345E,在变形温度1 000~1 100℃,变形速率1~10 s^-1时,单道次变形时变形温度和变形速度对临界应变和动态再结晶的影响,以及在变形温度950~1 050℃,变形速率10 s^-1双道次变形时变形温度和停留时间对静态再结晶的影响。试验结果表明,单道次变形时高的变形温度促进钢的再结晶,但高的变形速度加速钢的硬化;双道次变形时,停留时间延长和变形温度升高均增加静态再结晶百分率。     

Mathematical Model of Microstructure Evolution of X60 Line Pipe Steel During CSP Hot Rolling

An integrated process modelling system for simulating the microstructure evolution of Nb-microalloyed HSLA steel produced in CSP hot rolling process has been developed on the basis of the microstructure simulation and mechanical properties prediction technology. 3-D thermomechanical coupled finite element models for simulating hot strip rolling have been developed and the distribution of equivalent plastic strain through the thickness direction of the rolled material by CSP roiling was obtained. Thus the distribution of temperature, strain and strain rate through the thickness of the steel stocks, as well as the microstructure evolution during hot rolling of X60 line pipe steel strip has been investigated by using the developed integrated process modelling system. In addition, the determination and op-timization of controllable process parameters during CSP hot strip rolling for the Nb-microalloyed X60 line pipe steel have been implemented, and control strategies such as adopting larger pass reduction in the first stand, arranging ap-propriate pass interval times and proper rolling speed, to reduce or eliminate mixed grain microstructure of Nb micro-alloyed strip in CSP processing have been proposed.     

Hot Tearing Modeling: A Microstructural Approach Applied to Steel Solidification

Hot tearing during solidification processes has been deeply investigated in past and recent years through testing, modeling, and development of a number of macroscopic hot tearing criteria. The objective is predicting the crack occurrence during industrial solidification processes, which, in the steel production, are mainly ingot and continuous casting. The present work is inspired by the criterion proposed in the work of Bellet et al.[1] called CBC criterion, from which the methodological approach and experimental data used for calibration, related to nine carbon steels, have been derived. The proposed hot tearing criterion adopts as parameters: primary and secondary arm spacing, the mechanical resistance near the solidus temperature, the solidification parameters G (gradient) and v (dendrite tip velocity), the brittle range extension in the dendritic front and the temperature of formation of manganese sulfides. The new formulation is an attempt to substitute to brittle temperature range and steel content, appearing in the CBC criterion, the dendritic structure characteristics, in the aim of: (a) moving toward a generalized expression of the cracking index applicable to different steel classes; (b) introducing the dependence of the crack susceptibility on the cooling conditions. The agreement of the new hot tearing index values with the experimental ones is of the same kind as that of the CBC criterion, indicating that the parameters and the dependences adopted in the new criterion make a sense. Further study and experimental work are needed to assess the influence of the microstructure morphology on the hot cracking sensitivity and to check the suitability of the approach to a wider range of steel compositions.     

Asymmetric Rolling of Interstitial-Free Steel Using Differential Roll Diameters. Part I: Mechanical Properties and Deformation Textures

IF steel sheets were processed by conventional symmetric and asymmetric rolling (ASR) at ambient temperature. The asymmetry was introduced in a geometric way using differential roll diameters with a number of different ratios. The material strength was measured by tensile testing and the microstructure was analyzed by optical and transmission electron microscopy as well as electron backscatter diffraction (EBSD) analysis. Texture was also successfully measured by EBSD using large surface areas. Finite element (FE) simulations were carried out for multiple passes to obtain the strain distribution after rolling. From the FE results, the velocity gradient along selected flow lines was extracted and the evolution of the texture was simulated using polycrystal plasticity modeling. The best mechanical properties were obtained after ASR using a roll diameter ratio of 2. The textures appeared to be tilted up to 12 deg around the transverse direction, which were simulated with the FE-combined polycrystal plasticity modeling in good agreement with measurements. The simulation work revealed that the shear component introduced by ASR was about the same magnitude as the normal component of the rolling strain tensor.     

Role of Twinning on Dynamic Recrystallization and Microstructure During Moderate to High Strain Rate Hot Deformation of a Ti-Modified Austenitic Stainless Steel

This article discusses the role of twinning on dynamic recrystallization (DRX) and microstructural evolution during moderate to high strain rate (0.1 to 100 s⁻¹) hot deformation (1173 to 1373 K (900 to 1100 °C) range) in a Ti-modified austenitic stainless steel (alloy D9). The extent of DRX increased with increasing strain rate and temperature in the range of hot working parameters employed in the present study. The acceleration of DRX with strain rate is attributed to increased rate of dislocation accumulation during high strain rate deformation as well as adiabatic temperature rise. The DRX grains were found to be twinned and a linear relationship was observed between the area fraction of DRX grains and the fraction of Σ3 boundaries. Analysis of misorientations revealed that the majority of these Σ3 boundaries are newly formed coherent twin boundaries during DRX. Interaction of pre-existing Σ3 boundaries that may regenerate new Σ3 boundaries did not seem to occur frequently during DRX. The majority of the twin boundaries are found within the DRX grains, signifying that these annealing twins are mainly formed by “growth accidents” during the expansion of the DRX grains. It is suggested that annealing twins play an important role during nucleation and subsequent expansion of the DRX process in alloy D9.     

A Transient Thermal Model for Friction Stir Weld. Part I: The Model

Current analytical thermal models for friction stir welding (FSW) are mainly focused on the steady-state condition. To better understand the FSW process, we propose a transient thermal model for FSW, which considers all the periods of FSW. A temperature-dependent apparent friction coefficient solved by the inverse solution method (ISM) is used to estimate the heat generation rate. The physical reasonableness, self-consistency, and relative achievements of this model are discussed, and the relationships between the heat generation, friction coefficient, and temperature are established. The negative feedback mechanism and positive feedback mechanism are proposed for the first time and found to be the dominant factors in controlling the friction coefficient, heat generation, and in turn the temperature. Furthermore, the negative feedback mechanism is found to be the controller of the steady-state level of FSW. The validity of the proposed model is proved by applying it to FSW of the 6061-T651 and 6063-T5 aluminum alloys.     

新钢1580mm热轧线A572Cr.50瓢曲的分析

对新钢热连轧厂钢种A572Cr.50实际生产中出现的瓢曲问题进行分析,发现带钢存在性能不均匀、同板组织偏差大等现象,这些问题主要是层流冷却中存在冷却不均、工艺温度设定不合理等原因造成的.通过改进层流冷却装置、优化成分和调整工艺温度等措施,A572Gr.50瓢曲明显改善.